1. Field of the Invention
The present invention relates to a linear transfer mechanism and also to a transfer robot incorporating a linear transfer mechanism. In particular, the present invention relates to a transfer robot configured to move thin works such as a substrate along a straight path.
2. Description of the Related Art
Conventional transfer robots include a type that incorporates a linear transfer mechanism for moving a hand or hands along a straight path. These robots, which are simpler in construction and less expensive than multi-joint robots, are widely used in the field of e.g. manufacturing semiconductor devices or liquid crystal display panels, in which thin works such as wafers and glass substrates are brought into and out of various process chambers.
The linear transfer mechanism used for these transfer robots may be of a link-arm type using a combination of two parallelogram links (see JP-A-H10-6258 for example). According to the link-arm type transfer mechanism disclosed in JP-A-H10-6258, the two parallelogram links are connected with each other via a gear mechanism. Specifically, when the first parallelogram link pivots through a predetermined angle, the gear mechanism causes the second parallelogram link to pivot through twice the angle. The second parallelogram link is provided, at an end thereof, with a hand for carrying a work. With such an arrangement, when the main shaft of the main link arm in the first parallelogram link is rotated, the hand moves along a linear path, with its orientation maintained, over a distance range, i.e. from the state shown in FIG. 1 of JP-A-H10-6258, in which the link arm is folded, to the state shown in FIG. 2, where the link arm is extended.
Recently, wafers used for making semiconductors tend to have larger diameters. Likewise, in the field of liquid crystal displays, the panel size tends to become larger. In light of these trends, the size of the robot's hand and the size of the work to be transferred have been increasing, the transfer path has been getting longer. However, these trends have caused a problem that a link arm such as the above-mentioned two parallelogram link type is distorted in the vertical direction by the weight of the work and the hand, especially when the link arm is extended. Unfavorably, this makes it difficult to provide an accurate linear transfer movement.
Another type of linear transfer mechanism is disclosed in JP-A-2006-123135. This linear transfer mechanism, which is of non-link-arm type, includes a pair of straight guide rails on which a transfer carriage is disposed to be driven by a belt drive mechanism. In this linear transfer mechanism, the transfer carriage is moved by the belt drive mechanism along a straight path on the guide rails. With this arrangement, it is possible to cope with the need for a longer transfer path simply by increasing the length of the guide rails.
JP-A-2006-123135 also discloses a transfer robot. This transfer robot, including the above-described linear transfer mechanism, is used for manufacturing processes of semiconductor devices or liquid crystal display panels. Specifically, the transfer robot is configured to move a work into and out of process chambers. The conventional transfer system disclosed in the document includes an atmospheric transfer module and a vacuum transfer module through which a work is moved into and out of each process chamber. The vacuum transfer chamber includes a transport chamber around which a plurality of process chambers are arranged, and a loadlock which connects the atmospheric transfer module and the transport chamber to each other. A linear transfer robot capable of operating in a vacuum is installed in the transport chamber. The linear transfer robot receives a work in the loadlock, brings the work into the transport chamber, and then puts it into a selected one of the process chambers. At the same time, the transfer robot takes a processed work out of the process chamber and transfers it back to the loadlock.
As shown in FIG. 5 of JP-A-2006-123135, the transfer robot includes a fixed base for supporting the linear transfer mechanism. The linear transfer mechanism is provided with a guide member which is rotatable about a swivel axis with respect to the base, and vertically movable along the axis. JP-A-2006-123135 also discloses another linear transfer mechanism including two transfer carriages (hands), one disposed above the other, each supported by a set of guide rails. These two transfer carriages are driven independently by the belt drive mechanism. With such an arrangement, since the two hands can be driven independently, it is possible to improve the work transfer efficiency with respect to the process chambers. The inside of the base is hermetically sealed from the outside. In the base, four motors are placed at appropriate positions serving as power sources for the sliding movement of the two transfer carriages driven by the linear transfer mechanism, the swivel movement of the guide member, and the vertical movement of the guide member. With this arrangement, even if the transfer robot is used in a vacuum, the power supplying motors are in a sealed space (the inside of the base) separate from the vacuum environment. This eliminates need to use motors such as those built specially for use in a vacuum, while offering an advantage of using ordinary motors which are made for use in normal atmospheric environment.
As described above, according to the linear transfer mechanism and the transfer robot disclosed in JP-A-2006-123135, a high level of efficiency is achieved by independent driving of the two hands and eliminating needs for special motors for use in a vacuum. On the other hand, the motors which drive the transfer carriages are housed inside the fixed base, and the transfer carriages which receive the driving power from the motor make their travel on a straight path on the guide member supported by the base. With this arrangement, the drive mechanism that transmits the drive power from the motor to the transfer carriages needs to transmit the power over a long distance, and its structure tends to become complicated. Also, the long power transmission route may give rise to a greater power transmission loss in the drive mechanism.